dc.description.abstract |
Mosquito saliva plays a central role in blood meal acquisition plus the
development and transmission of the malaria parasite. Functional genomics and
proteomics studies have characterized and predicted roles of many proteins in the
sialotranscriptome of An. gambiae and their predicted roles. Whereas, this approach
provides important insights or a priori on the role of saliva and its interaction with
Plasmodium in the midgut, the large amounts of data often presents a problem in
determining the best strategy for exploiting the knowledge in malaria control. For this
reason, a series of experiments was designed to test and validate several a priori in
this study: 1) Saliva contains antimicrobial proteins (AMPs) that may modulate
bacteria population dynamics in the midgut thus affecting mosquito survival; 2) Saliva
contains several catabolic enzymes and protease suppressors thus affecting
Plasmodium development during blood meal digestion and 3) Saliva contains
xanthurenic acid and other molecules whose role remains unknown that may directly
or indirectly affect Plasmodium development in the midgut.
Surprisingly, mosquito salivary gland homogenate (SGH) of female
mosquitoes did not exhibit any antimicrobial activity when tested against 8 bacteria
species previously isolated from An. gambiae midgets indicating no role for saliva in
modulation of endosymbiont bacteria in the midgut. Whereas bacteria was found to be
crucial in the larval diet for survival and development in the immature stages, the role
of endosymbiont bacteria in the adult mosquito proved ambivalent as it varied from
beneficial to harmful under various experimental setups. However, the clear role in
xxi
larval survival and development indicates the employment of biological controls such
as Bti and Bs is a winning strategy that should be promoted in integrated vector
management. Lastly, SGH was demonstrated to have protease suppression properties
that suppressed both the serine proteases and aminopeptidase. Interestingly, P.
falciparum was also shown to modulate proteases by down-regulating serine proteases
and up-regulating aminopeptidase, which was recently discovered as a Plasmodium
receptor during midgut invasion. SGH suppression of aminopeptidase therefore
suggests a possible role for SGH molecules in transmission blocking, however oocsyt
counts in mosquitoes fed on infective blood meal + SGH did not differ significantly
when compared to control group fed on infective blood meal only. |
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